Power transmission



Dec. 31, 1946.

A. L. ELLIS I 'POWER mnsmIssxon Filed Jan. 14. 1936 7 Sheets-Sheet 1 INVENTOR AII'NUI L. ELus ATTORNEY Dec. 31, 1946. I 5 I 2,413,301

POWER TRANSMISSION Filed Jan. 14, 1936 7 Sheets-Sheet 2 INVENTOR ARTHUP L. 81.0.15

ATTORNEY Dec. 31, 1946. A. ELLIS 2,413,301

'POWER TRANSMISSION Filed Jan. 14, 1936 I '7 Sheets-Sheet 3 lNVENTOR ARTHUR L. ELLIE ATTORNEY Dec. 31, 1946.

A. ELLIS POWER TRANSMISSION Filed Jan. 14, 1936 7 Sheets-Sheet 4 lllllllllllll INVENTOR Anmurr L. ELLIS 1 ATTORNEY Dec. 31, 1946, 4 A. L. ELLIS 2,413,301

POWER TRANSMISS ION Filed Jan. 14, 1936 7 Sheets-Sheet 5 INVENTOR Am'uun L. ELL/s M z. T

ATTORNEY Dec. 31, 1946. A. L. ELLIS 2,413,301

POWER TRANSMI SSION Filed Jan. 14, 1936 7 Sheets-Sheet 6 INVENTOR ARTHUR L. ELL/5 BY ATTORNEY Dec. 31, 1946. s I 2,413,301

POWER TRANSMISS ION Filed Jan. 14, 1936 7 Sheets-Sheet 'T INVENTOR Anruw L. Enos ATTORNEY Patented Dec. 31,194

UNITED. STATES PATENT OFFICE rowan rmnsmssron Arthur L. Ellis, Deep River, Gonn assignor, by mesne ents, to Vlckers Incorporated, Detroit, Mich, a corporation of Michigan Application January 14, 193.6, Serial No. 59,072

16 Claims. (CI. 60-53) 1 This invention relates to power transmissions,

particularly to control devices for power transon the driven member while the ratio of power transmission is such that the driven member moves at a high speed relative to the driving member, the mechanical advantage of the driving member in overcoming this load is small, so that the prime mover becomes easily overloaded under these conditions.

Since the variable speed powertransmission in itself provides a means for increasing the mechanical advantage of the driving member over the driven member, it is an object of the present invention to provide control means operative to change the ratio of power transmission upon the occurrence of an excessive load on the driven member in such a way that the power transmis. sion itself will act to prevent transmission of the overload to the driving member.

A further object is to provide in a power transmission of the character described a control means responsive to the application of a predetermined amount of torque to the driving member for increasing the mechanical advantage of that member over the driven member.

A further object is to provide a novel control system of the character described including a fluid motor having a. difierential piston and a pair of control valves therefor, one of which is operable to determine the operativeness or nonoperativeness of the piston and the other of which is operable to determine its direction of movement.

Further objects and advantages of the present invention will be apparent from the following description, reference being had to the accompany-.

ing drawings wherein a preferred form of the present invention is clearly shown.

In the drawings:

Fig. 1 is a diagrammatic illustration of a fluid .circuit embodying one form of the present in vention.

Figs. 2 and 3 are views corresponding to Fig. 1 showing the parts in diflerent positions.

Fig. 4 is a cross section on line 4-4 of Fig. 5 showing the control valves with their operating mechanisms partly inelevation.

Fig. 5 is a cross section on line 5-5 of Fig. 4.

Fig. 6 is a cross section on line 6-5 oi Fig. 4.

Fig. 7 is a fragmentary perspective view of a portion of the valve control mechanism.

Fig. 8 is a top view partly in section of the power transmission mechanism and a portion of the control system. I

Fig. 9 is a fragmentary sectional view on line 9-9 of Fig. 8.

Fig. 10 is a fragmentary sectional view on line Iii-i B of Fig. 8.

Referring now to Fig. 8, there is illustrated a power transmission of the well-known Waterbury type comprising a variable displacement pump or A-end" I 0 and a fixed displacement hydraulic motor or B-end l2. Transmissions of this character are fully described in the patents to Williams 1,044,838 and to Janney 1,020,285, so that it is unnecessary to describe the construction of the transmission itself in detail. For the purpose of this specification it may be stated that the A-end l0 comprises a drive shaft l4, rota.- tion of which causes fluid to be pumped to the "B-end l2. The displacement of the pump and consequently the quantity of fluid pumped per revolution of shaft l4 are regulated'by a tilting box I which is shown in the neutral position. Movement of the tilting box in a clockwise direction away from the neutral position produces forward rotation of the "B-end and its driven member l8 (arrow A), while movement of the tilting box counter-clockwise away from the neutral position causes rotation of .the driven member l8 in the opposite direction. While the position of the tilting box IE may be controlled in any suitable manner, in the form of the invention illustrated,

a. control mechanism ofthe type shown in the patent to Janney 1,220,424 is utilized and includes a non-rotati've rod 20 mounted for sliding movement in bearings 22 and 24 and having a sliding and pivoting connection at 26 with a stud 28 on the tilting box IS. A screw shaft 30 is connected .to the shaft 20 by a. swivel 32 and at its opposite end carries a splined head 34 which is slidable but not rotatable relative to a slotted sleeve 36 (see Fig. 9); The sleeve 36,is journalled on bearings 38 and 40 and has a project-.

ing shaft 42 upon which is mounted a hand wheel movement. The pitch of the threads of shaft 36 piston 68 operating in a-cylinder 58 by which the rod 20 and tilting box I8 may be operated directlywith fluid under pressure.

An. A-end driving shaft I4 carries a double clutch 80 having a movable member 62 Splined to the shaft I4 and slidable to engage either a clutch member 64 rigidly secured to a shaft 66 or a clutch member 68 rotatably mounted on the shaft I4. The shaft 68 may be that of any suitable prime mover, for example an electric motor, not shown, and is used for normally driving the power transmission. The clutch member 68 carries a sprocket 18 which is driven by a chain 12 from a manual drive clutch unit 14 by which the A- end" may be driven by hand from a hand crank 18 upon failure of-power. at the shaft 66.

Means for moving the tilting box toward neutral position upon occurrence of an overload is provided and includes a housing 18 mounted on top of the A-end" directly over the upper trunnion upon which the tilting box I6 is mounted. Referring now to Fig. 4 the housing 18 carries a removable bearing 80 within which a stub shaft 82 is mounted. The lower end of the shaft 82 is adapted to be coupled directly to the tilting box by means of a keyway 84. Shaft 82 has rigidly secured thereto an arm 86 carrying a cam 88 for the purpose of controlling a constant horsepower control valve generally designated at 80. Shaft 82 also carries an arm 82 having a lost motion connection with a cam bar 84 for the purpose of operating a directional control valve generally designated at 86. The valves 90 and 86 are formed within a valve block 88 secured to one side of the housing 18. Valve block .88 also includes a constant torque valve I00 (Fig. 5) which is operated from the clutch unit 14 shown in Fig. 8.

Referring now to Figs. 6 and 7, cam 88 is formed with a high portion I02 at its mid-part corresponding to neutral position of the tilting box I6 and curved portions I04 and I06 sloping away from the high part I02 symmetrically on either side thereof. A roller cam follower I08 is'pivoted on a lever IIO, the latter being pivoted at H2 in a bracket II4 formed on the valve block 88. The outer end of the lever IIO carries a link II8 pivotally connected to a tension rod II8 having an adjustable spring plate I20 at its outer end abutting a spring I22. The spring plate I20 is moved to the right in Fig. 6 whenever the arm 86 moves away from the neutral position illustrated. thus decreasing the compression of the spring I22. The left-hand end of spring I22 abuts against a spool I24 which in turn abuts against a valve member I26 slidably mounted within a bore I26 formed in the valve block 88. The left-hand end of the valve member I26 is reduced in diameter at I30 to fit a reduced portion I82 of the bore I28. There is thus provided a small area against which fluid pressure may be exerted through a port I34 to counteract the force of the spring I22 and to move the valve I 26 to the right in Fig. 6. A port I36 is provided leading to the bore I28 and is so positioned that a predetermined amount of movement of the valve I26 to the right opens a connection between the port I34 and the port I86. The valve I26 is also provided with a reduced I48 with 8. port [42 in the position illustrated and to close off the port I40 when valve I26 moves to the right sufllciently to open port I 88. A closure I48 protects the spring I22 and seals the end of bore I28.

Referring now to Fig.5, the directional control valve 86 includes a valve member I44 slidable in a bore I46 formed in the valve block 98 and having an end closure I48 at its outer end. The valve 'member I44 is operated from the arm 82 by means of the cam bar 84 having a cam portion I60 which cooperates with a pin I52 formed on a lever arm I64. The arm I64 is pivoted at I56 to a bracket I58 formed in the housing 18 and carries an adiustable stop screw I60 :for determining the left-hand positionof the valve I44. The arm I54 also carries a pin I62 which projects through a slot I64 in'the bar 84 I for the purpose of preventing the cam bar 64 from lifting away from the pin I62 and also for positively moving the arm I64 to the left when the cam bar 84 reaches the left-hand limit of its-travel. The cam bar 84 is connected to the arm 82 by means of a pin I86 carried by the cam bar 84 and a slot I68 formed in the arm 82. A spring I10 abuts against a pin I12 on the arm 82 and a pin I14 on the cam bar 84 and tends to keep pin I66 in the left-hand end of slot I68.

The mechanism is so arranged and adjusted that in the position illustrated which corresponds to neutral position of the tilting box I6 the valve I44 is maintained in its left-hand position by the spring I10 actingthrough the pin I14, cam bar 94, the right-hand end of the slot I64, the pin I62, and the lever I54. Movement of the arm 92 away from the position illustrated in a clockwise direction in Fig. 5 does not-move the cam bar 84 but merely increases the tension in the spring I10; the slot I68 permitting clockwise overtravel of the arm 82. Should the arm 92 move counter-clockwise away from the position illustrated, the left-hand end of slot I68 abuts pin I66 moving cam bar' 84 to the right.

Cam I50 thus moves the pin I62 downwardly causing a clockwise movement of the arm I64 and moving valve I44 to the right. The construction is such that the complete travel .of valve I44 takes place in a very small angle of movement of the arm 92 as compared with its total movement.

The bore I46 of the valve I44 has a port I18 at its left-hand end and a port I18 to the right thereof. Valve I44 is formed with a reduced portion I adapted to connect the ports I16 and I18 when the valve is moved to the right. A bore I82 is formed centrally of the member I44 and connects by means of a cross bore I84 the right-hand end of the bore I46 with the interior of the housing 18. In the position illustrated in Fig. 5, the port I18 is in communication with the right-hand end of tne bore I48 by means of a reduced portion I86 formed on the valve member I44 and is, therefore, in communication with the interior of the housing 18 when the valve is in the position shown. This communication is cut oil by the valve I44 being moved to the right.

Th constant torque valve I68 includes a valve member I88 slidably mounted within a bore I88. The bore I80 is formed with a port I82 communicating with the port I16 through a conduit I84 and a port I96 communicating with the port I42 of valve 90 through a conduit I98. The valve I88 is formed similarly to the valve I44 except that it is operated by means of a stem 200 projecting outwardly from the valve block 98 through a packing gland 202. A bracket 204 carries a lever 206 having pivotal connection at 208 with the stem 200 and at 2I0 with an operating rod 2I2. In the position illustrated in Fig. 5 the valve I88 closes off communication between ports I92 and I96 and connects port I96 to the interior of housing 18. When the valve is moved to the right, the ports I92 and I96 are connected together and port I96 is cut off from communication with the housing 18.

The clutch unit 14 illustrated in Fig. 8 includes,

a main shaft 286 carried in bearings 268 and rigidly secured to the crank 16. Shaft 286 carries a hub 290 rigidly secured thereto which drives a set of planetary pinions 292 cooperating with a fixed ring gear 294 and a sun pinion 296. The sun pinion 296 is rigidly secured to a flywheel 298 journalled on the shaft 286 by means of bearings a projection 3| 2 engaging with a cam surface 3M.

formed in the hub of a sprocket 3I6 which is mounted on the hub member 306 so asto be rotatable relative thereto. Cam member 308 has a slot 3I8 formed therein for engagement with-a fork 320 which is pivotedly mounted on a shaft 322. Shaft 322 has a lever 324 connected by means of a linkage 326 to the operating rod 2I2 for the constant torque valve I00.

It will be seen that the crank 16 is directly geared to the flywheel 298 in a manner to cause the flywheel to revolve at a greater rate of speed than the crank 16. The clutch 304 connecting the shaft 286 to the rotatable hub 30s is ar-' ranged to slip when a predetermined amount of torque is applied thereto. The force of the springs 3I0 is so proportioned relative to the torque transmitted by the clutch 304 that the projection 3I2 may move substantially half the length of the cam surface 3I4 before springs 3I0 are compressed sufficiently to require a torque or, when the-hand wheel 44 is being used for normal control, with sufilcient force to overcome the greatest manual effort which can be applied to wheel 44.

Fluid under pressure for operating the piston 56. under the joint control of the valves 90, 96.

I00, 2I4, and 2I6 is provided from two alternate sources: The first is the power circuit of the hydraulic transmission itself the valve plate thereof being indicated at 222. Conduits 224 and 226 connect with each of the two valve ports 228 and 230, respectively, and lead to a shuttle valve 232 for the purpose of connecting a conduit 234 with whichever of the conduits 224 and 226 has a higher pressure at a given instant. The other source comprises an auxiliary pump 236, of any suitable construction, having an intake 238 leading from the expansion tank,not shown, and having a relief valve, not shown, which are customarily provided with hydraulic systems of this character. Pump 236 may be driven, for example, by an electric motor 240'. Pump 236 has an outlet conduit 242 communicating with a shuttle valve 244 for the purpose of selectively delivering to a conduit 246 fluid from either conduit 234 or conduit 242 to the port 252 of the valve 2I4. Conduit m the operating rod 2I2 for the constant torque valve I00.

Referring now to Fig. 1, the hydraulic circuit for the control mechanism of the present invention includes the mechanism above described, and in addition, a pilot control valve 2I4 and a hydraulically operated valve 2I6 both of which are formed in a second valve block 2I8 formed in the body of the cylinder 58 (see Fig. 8). The pilot control valve 2 I4 may be operated by a hand lever 220 or by any suitable automatic mechanism desired, and is arranged to move the piston 56 and tilting box I6 to the right when in the position illustrated,'and to move the same to the left communicates by means of a branch 264 with the conduit I94 connecting ports I16 and I92 of valves 96 and I00 respectively, and has a second branch 256 leading to a port 253 of the valve 2I6. Valve 2 I6 is formed with a port 260 communicating by means of a conduit 262 with the small end of the cylinder 58 and, in the position of the valve 2I6 illustrated, the ports 250 andl260 are connected. When the valve 2 I6 is moved to the right by a spring 264, the port 260 is cut oil from communication with the port 258 and placed in communication with a port 266 communicating with valve 2I6. In the position illustrated in Fig. 1

the valve 2I6 is arranged to connect the port 210 with a port 212 leading by means of a conduit 214 to the large end of the cylinder 5.8. When the valve 2I6 is moved to the right as in Fig. 3, port 212 is cut oif from communication with port- 210 and connected with a port 216 leading to a port 218 of the valve 2I4. Port 218 is connected with the po t 252 by the valve 2I4 in the position illustrated in Fig. l. Whenvalve 2I4 is moved to its mid-position, the port 218 is cut ofi from communication with any port in the valve 2I4. When moved to the limit of its travel to the left, valve 2I4 connects port 218 with a port 280 leading to the expansion tank, not shown. Conduits 26I and 203 connect the opposite ends of the valve 2I4 to the expansion tank to eliminate trapping effects. The ports I36 and I40 of valve are connected together by means of a conduit 282 leading to an operating cylinder 284 at the right-hand end of valve 2 I8 for overcoming the force of the spring 284 and moving the. valve 2" into the position illustrated in Figures 1 and 2.

In operation, the transmission being suitably assembled with the shaft 88 connected to a prime mover, preferably one of constant speed, and the shaft I8 being connected to a load which it is desired to drive at variable speeds, the clutch 88 is shifted to engage the clutch member 84. If it is desired to operate the "B-end" shaft I8 and the load to a predetermined position, that is by "follow-up control the hand wheel 44 is turned causing the screw shaft 88 to move axially in the nut 48 moving the tilting box out of neutral position. Fluid is thus pumped from the "A-end" to the B-end" and the latter operating as a fluid motor turns the shaft I8 and the load. -This movement of shaft I8 turns th nut 48 through the gears 88 and 84 in a direction tending to move the screw shaft 88 back into the position corresponding to neutral position of the tilting box in the manner more fully described in the Janney Patent 1,220,424. So long as handwheel 44 is turned the "B-end" shaft I8 will continue to turn at a corresponding speed and direction.

Alternatively the transmission may be operated under normal control of the pilot valve 2| 4 instead of under the controlof handwheel 44, if it is desired to drive the load continuously at a given rate of speed for considerable intervals. Thus,

during normal operation, when there is no tendency to overload the prime mover, which is illustrated in Fig. 3, the valve 2I8 lies in its righthand position, in which the small end of the cylinder 88 is constantly supplied with fluid under pressure through the conduit 282, ports 288 and 288, conduits 288 and 242, and pump 288. The large end of the cylinder 88 under these conditions is subject to control by the valve 2I4 through the conduit 214, and ports 212 and 218. Thus with the valve 2 in the position shown the port 218 is blocked and piston 88 is held stationary. With the valve 2I4 moved to the right, port 218 is'connected with conduit 282 for admission of fluid under pressure from the auxiliary pump 288 to the large end of the cylinder 88 causing piston 88 to move to the right and thus moving the tilting box in a clockwise direction in Fig. 8, and increasing the speed of the B-end in a forward direction. When the valve 2 is moved fully to the left. the port 218 is connected to port 288, thus exhausting fluid from the large end of the cylinder 88 causing the piston 88 to move to the left under the constant pressure supplied to the small end of the cylinder 88.. The speed of the B-end in a forward direction will therefore be reduced, or if the tilting box has been i moved to the left past neutral position the speed in the opposite direction will be increased. During operation under normal control of valve 2 the handwheel 44 is free totum with the "B-end" shaft I8. That is, with the pump "on stroke in any given position, the member 28 and tiltin box I8 will remain stationary while the gear 84 will rotate the gear 88 and nut 48 and carry along with them in their rotationthe screw shaft 88, the head 84, the sleeve 38, and the handwheel 44. as a unit, without imparting longitudinal movement to the member 28.

Should an excessive resisting load be imposed upon the shaft I8 such that the prime mover connected to the shaft 88 would be overloaded. the constant horsepower valve 88 operates to move the tilting box I8 toward neutral position. It is a characteristic of hydraulic trans- I 8 missions of the type. described that the fluid pressure in the working circuit of the transmission itself varies in direct proportion to the torque load imposed upon the B-end" shaft I8. When the shaft I8 is turning in one direction, one of the valve ports, for example 288, becomes the pressur port and the pressure existing in this port is transmitted to the conduit 228 and the shuttle valve 282. On rotation in the opposite direction the port 228 becomes the pressure port and the pressure therein is transmitted to conduit 224 and shuttle valve 282 which moves to the position opposite to that illustrated in Fig. 1. Any abnormal pressure rise that occurs ineither valve ort 228 or 288 is thus transmitted through conduits 284 and 248 to port I84 of the constant horsepower valve 88. When this pressure exceeds the value determined by the compression of the spring I22, the valve member I28 moves to the right opening port I88 and permitting the fluid to pass through conduit 282 to the power cylinder 284 of the valve 2I8. The opening of port I38 to pressure fluid from port I84 initiates a sequence of operations immediately causing a ratio of transmission to be established which will be safe for the particular overload imposed on the B-end" shaft I8. That is, the mechanical advantage of the A-end shaft I4 over the B- end shaft I8 is increased to the point where the rime mover is not overloaded..- The operation for this purpose is as follows:

Assuming that the tilting box is standing in a position for forward drive the piston 88 will be standing to the right of the mid-point of its travel as illustrated in Fig. l. The directional control valve 88 will also be in the position illustrated in Fig. 1 in which fluid flow is cut oil between the ports I18 and I18 and the port I18 is connected tothe interior of the housing 18 whichis 'maintained at atmospheric pressure by a connection to the expansion tank, not shown. The valve 2I8 having moved to the left, as illustrated, by the fluid pressure admitted to the power cylinder 284 by valve 88, connects the large end of control cylinder 88 to the tank through the conduit 214, port 212, port 218, conduit 288, port I18, and bore I82. Thesmall endof the cyl r 88 is supplied with fluid under pressure either from the main power circuit of the transmission or from the auxiliary pump 288. depending upon the position of the shuttle valve'244. The circuit for this fluid is from the shuttle valve 244 through conduit 288, port 288, valve 2I8, port 288, and conduit 282 to cylinder 88. The piston 88 thus moves to the left until the ratio of transmission is such that the prime mover 88 may handle the overload without danger.

The compression of the spring I22 is variedby the cam 88 in accordance with the-position of the tilting box I8 and the shape of the cam is such that the horsepower required at the shaft 88 when valve 88 opens is constant for all ratios of transmission. Since the horsepower transmitted by the hydraulic transmission is proportional to the product of the fluid .pressure existing in the transmission and the speed of the Bend shaft, the cam 88 may be so shaped that the compression of the spring I22 will be maintained at the proper value for any speed ratio of transmission. Thus when the B-end shaft I8 is revolving slowly, the pressure which may be built up without exceeding the limiting horsepower is high. Since the position of the tilting box I8 is determinative of the speed of the shaft I 8, it will be seen that when the tilting box I6 is near the neutral position the cam 88 holds the tension rod 8 to the left, as shown in Fig. 6, applying a relatively high force to the valve member I26. A relatively high pressure is therefore required to move the valve member I26 to the right under these conditions.

Conversely when the "B-end shaft I8 is revolving at a high speed, much lower pressure in the system will produce an overload on the prime mover so that with the tilting box in a high speed position, as shown in Fig. 1, the cam 88 applies a smaller force to the valve member I26 permit ting it to open on a much lower pressure. Thus the full horsepower of the prime mover may be utilized at low B end speeds without danger of overloading the prime mover at high B-end speed.

When the tilting box is in position for rotation of the B-end shaft I8 in the reverse direction, the parts take up th position illustrated in Fig. 2 wherein the piston '56 lies to the left of the mid-point of its travel and upon the occurrence of an overload itis necessary to move the piston to the right rather than to the left as previously described. The directional control valve 96 moves to the right during the first small increment of travel of the tilting box away from neutral position in a counter-clockwise direction in Fig. 1 and Fig. 8, and thereupon connects the port 210 of the valve 2 I 6 with the shuttle valve 244 through the conduits 268, I94 and 254. Fluid under'pressure is thus admitted from either the main power circuit or from the auxiliary pump 236 to the large end of the cylinder 58 from port 212 through conduit 214. Thus, whenever the "B- end shaft is rotating reversely and an overload occurs, the movement of valves 90 and 2I6 to the right and left respectively, admits fluid under pressure to both ends of the cylinder 58. Since the area of the piston 56 exposed to th lefthand end of the cylinder 58 is greater than the area exposed in the right-hand end, the resultant force tends to move the piston to the right toward neutral position until the mechanical advantage of the A-end shaft over the B-end shaft is increased sufliciently so that the prime mover may handle the overload imposed.

During operation with normal control exercised through valve 2I4, the operation of valve 98 causes this normal control to be temporarily interrupted since valve 2I6, in the position shown in Fig. 1, cuts off communication between conduit 218 and port 212. The cylinder 58 is thus cut off from any control influence by valve 2I4 until the valve 90 closes permitting valve 2I6 to move to the right into the position shown in Fig. 3. When normal control is exercised through valve 2I4, the handwheel 44 is free to turn with the B- enfd"'shaft I8; the shaft 30 and nut 46 turning together as a single unit at each particular setting of the control piston 56. When piston 56 moves, of course, the handwheel 44 speeds up or slows down relative to the "B-end shaft I8 so long as piston 58 continues to push or pull the threaded shaft 30 into or out of the nut 46. Dur-,

ing operation with normal control exercised through handwheel 44 instead of through valve 2| 4, that is during operation with follow-up control, the valve 90 takes control away from handwheel 44 whenever safe loads are exceeded. This comes about from the fact that the effort exerted by piston 56 when valve 90 opens is greater than any effort which can be manually applied to handwheel 44. Accordingly when valve 90 Opens, piston 56 moves toward neutral position 10 as just described, bringing with it the shaft 80.

In order to move, the shaft 30 must at least slow down relative to the "B-end" and may even stop or reverse. In any event the rotation of shaft 30 must be algebraically less than the rotation of the B-end shaft I8 and nut 46 in order to cause Operation under these conditions is identical to that previously described, the only difference being that if the port 230, for example, be the pressure port when power is transmitted normal- 1y through the transmission for a given direction of rotation of the shaft I8, then the port 228 becomes thepressure port when the load' tends to feed power back to the prime mover. Since the occurrence of an abnormal pressure rise in either port causes movement of the tilting box I6 toward neutral position, it will be seen that an excessive amount of power feed-back will reduce the mechanical advantage of the B-end" shaft I8 upon the A-end shaft, thus slowing down the B-end shaft and reducing the horsepower transmitted back to the A-end" shaft;

When the transmission is operated manually by the crank 16, as when a failure of the prime mover occurs, the horsepower which may be transmitted through the transmission is limited by the constant torque valve I00. Rotation of the crank 16 drives the shaft 286 which drives the flywheel 298 at a higher rate of speed through the planetary gearing 292, 294, 296 for steadying the speed of operation of the shaft 286, and also drives the sprocket 3I6 through the clutch 304 and through the spring-loaded cam mechanism 3I2, 3I4. Upon the occurrence of an overload sufficient to require an excessive torque upon the crank I6, the sprocket 3I6 slips relativeto the hub 366 causing the projection 3| 2 to travel along the cam surface 3I4 compressing the springs 3I0. As soon as the projection 3E2 has travelled along the cam surface 3I4 a predetermined distance, the

torque required for further travel exceeds the,

torque which the clutch 304 is capable of transthe torque required falls off to a safe value.

The movement of the cam member 398 to the left caused by the cam 3I4 actuates the fork 320 to pull the operating rod 2| 2 to the left in Figs. 1 and 8, thus moving the valve member I88 to the right and connecting port I96 to port I92 instead of to the tank. Fluid under pressure is thus admitted from the shuttle valve 244 through the ports I92 and I96, conduit I98, ports I42 and I 40 and the conduit 282 to the power cylinder 284, moving valve 2I6 to the left-hand position illustrated in Fig, l. The piston 56 is thus caused to move toward neutral position in the manner preyiously described in connection with the constant the A-end shaft l4 over the 'B-end" shaft is until the ratio of power transmission is such that the overload may be safely handled at the crank 18. Since the power delivered-to the crank 18 is ordinarily less than that of the prime mover, the constant horsepower valve 80 will not operate for limiting loads which are excessive when the transmission is driven from the crank 16. In other words, it is desirable that the settings of the operating mechanism for the constant horsepower valve Sll and the operating mechanism for the torque limiting valve lilll be such that the valve lllli comes into operation at a mugh lower load on the shaft l8 than does the constant horsepower valve 90. The operation of the constant torque valve is subject to the directional control valve 85 in the same manner as is the constant horsepower valve SI. Thus, whenever the tilting box lies on the counter-clockwise side of neutral position in Fig. 8, valve 98 will lie to the right in Fig. l and connect the large end of cylinder 58 to pressure fluid whenever valve Iii is moved to the left by pressure fluid from valve III. This circuit is through conduit 25!, port ili, valve SI, port I18, conduit 2", port 21!, valve ZIG, port 212 and conduit 214. The greater area of the large end of cylinder BI is thus predominant over the area at the small end and piston 56 is thereby moved to the right toward neutral position.

It will thus be seen that the present invention provides a control device for a variable speed transmission whereby the transmission itself will automatically prevent the overloading of its prime mover regardless of the resisting load applied to the driven member of the transmission.

While the form of embodiment of the invention as herein disclosed, constitutes a preferred form, it is to be understood that other forms might be adopted, all coming within the scope of the claims which follow.

What is claimed is as follows:

1. In a power transmission device the combination of a driving,shaft, a driven member, a variable speed hydraulic transmission for delivering power from the driving shaft to the driven.

member, a member movable to vary the me-- chanical advantage of the driving shaft upon the driven member, follow-up control means for normally determining the position of said member, fluid pressure operated means for moving said movable member, a valve responsive to excessive fluid pressure in' the hydraulic transmission for controlling the fluid pressure operated means, and means for increasing the pressure response of said valve in accordance with changes in the position of the movable member tending toward increased mechanical advantage.

2. In apower transmission device the combination of a driving shaft, a driven member, a variable speed hydraulic transmission for delivering driven member and including means forming a source of pressure fluid, a member movable in either direction away from a neutral position for varying the speed and direction of the driven member relative to that of the driving member, means including a diflerential piston and cylinder for operating said movable'member, a valve for power from the driving shaft to the driven memher, a member movable to vary the mechanical advantage of the driving shaft upon the driven member, control means for normally determining the position of said .member, fluid pressure operated means for moving said movable member to increase said mechanical advanta e upon excessive pressure being developed within the hydraulic transmission, and means for operating the flrst mentioned means in response to pressure so as to maintain a predetermined maximum value for the product of fluid pressure and driven member velocity.

3. In a power transmission device the combination of a driving shaft, a driven member,'a reversible variable speed power transmission for delivering power from the driving shaft o the controlling the admission of fluid from said source to both ends of said cylinder and a second valve for cutting of! fluid from the large end of the cylinder in cooperation with the flrst mentioned valve and means for operating the second valve as the movable member passes through the neutral position.

4. In a power transmission device the combination oi a driving shaft, a driven member, a reversible variable speed power transmission for delivering power from the driving shaft to the driven member, a member movable in either direction away from a neutral position for varying the speed and direction of the driven member relative to that of the driving member, means including a dlfl'erential piston and cylinder for operating said movable member, a valve selectively operable to cause the flow of pressure fluid to move said piston and-a second valve operable to selectively determine the direction or movement of the piston under the influence of flrst mentioned valve, and means for operating the second valve as the movable member passes through the neutral position, said last named means including a cam operable by said movable member to actuate the valve through its full stroke by a slight movement of the movable member.

tion of a driving shaft, a driven member, a reversible variable speed power transmission for delivering power from the driving shaft to the driven member, a member movable in either direction away from a neutral position for varying the speed and direction of the driven memrelative to that of the driving member, means including a differential piston and cylinder for operating said movable member. a valve foricontrolling the admission of fluid to both ends of said cylinder, second valve for cutting oi! fluid from the large end of the cylinder in cooperation with the first mentioned valve, means for op-.

erating the second'valve as ,the movable member passes through the neutral position, said last named means including a cam operable by said movable member to actuate the valve through its full stroke by a slight movement of the movable member, and a lost motion connection between the cam and the movable member.

6. In a power transmission device the combination of a driving shaft, a driven member, a reversiblevariable speed power transmission for delivering power from the driving shaft to the driven member, a member movable in either direction away from a neutral position for varying the speed and direction of the driven member relative to that of the driving member, means including a fluid motor for operating said member, a valve selectively operable to cause flow of pressure fluid to move said motor, a second valve in series with the flrst valve for selectively determining thelivering power from the driving shaft to the drivenmember, a member movable to vary the mechanical advantage of the driving shaft upon the driven member, means responsive to the pressure in said transmission for moving said member, and means movable with said member for increasing the pressur response of said means as the member is moved toward the position of maximum mechanical advantage.

8. In a variable speed fluid power transmission device the combination of a variable displacement pump, a fluid motor driven by the pump, means 'for driving the pump, means for regulating the pump displacement in response to pressure changes produced at the fluid motor and means for increasing the response of the regulating means in accordance with decreases in the displacement of the pump.

9. In a power transmission device the combination of a driving shaft, a dri"en member, at variable speed hydraulic transmission for delivering power from the driving shaft to the driven member, a member movable to vary the mechancal advantage of the driving shaft upon the driven member, control means for normally determining the position of said member, means for moving said movable member to increase said mechanical advantage upon excessive pressure being developed within the hydraulic transmission, said means responding to higher pressures at lower speeds of the driven member.

10. In a power transmission system the combinatlon of a driving shaft, a driven member, a variable speed power transmission including a pump operable from the driving shaft, 9, motor operable by fluid delivered by the pump and connected to actuate the driven member, locally operable manual means for controlling the flow of fluid from the pump to the motor, additional means for controlling the flow of fluid from the pump to the motor and including a servo-motor and a pilot control valve therefor, protective means including a, valve connected to exercise control over said servo-motor during overload independently of the other controlling means, and torque responsive means for operating said valve.

11. In a power transmission system the combination of a driving shaft, a driven member, a variable speed power transmission including a pump operable from the driving shaft, a motor operable by fluid delivered by the pump and connected to actuate the driven member, locally operable manual means for controlling the flow of fluid from the pump to the motor, additional means for controlling the flow of fluid from the pump to the motor and including a servo-motor and a pilot control valve therefor, and protective means including a valve connected to exercise control over said servo-motor during overload independently of the other controlling means, and pressure responsive means for operating said valve.

12. In a power transmission system the combi- I nation of a driving shaft, a driven member, a

variable speed power transmission including a pump operable from the driving shaft, a motor operable by fluid delivered by the pump and connected to actuate the driven member, locally operable manual means for controlling the flow of fluid from the pump to the motor, additional means for controlling the flow of fluid from the pump to the motor and including a servo-motor and a pilot control valve therefor, and protective means including a valve connected to exercise control over said servo-motor during overload independently of the other controlling means, and means for operating said valve in response to pressure so as to maintain a'predetermined maximum value for the product of fluid pressure and driven member velocity.

13. In a power transmission device the combination of a driving shaft, adriven member, a variable speed hydraulic transmission for delivering power from the driving shaft to the driven member, a member movable to vary the mechanical advantage of the driving shaft upon the driven member, control means for normally determining the position of said member, means for moving said movable member to increase said mechanical advantage upon excessive pressure being developed within the hydraulic transmission and including means for disconnecting said normal control means.

14. In a power transmission device the combination of a driving shaft, a driven member, a variable speed hydraulic transmission for delivering power from the driving shaft to the driven member, a member movable to vary the mechanical advantage of the driving shaft upon the driven member, control means for normally determining the position of said member, means for moving said movable member to increase said mechanical advantage upon excessive pressure being developed within the hydraulic transmission and including means for disconnecting said normal control means, and means for increasing the pressure response of the second mentioned means in accordance with decreases in the speed of the driven member.

15. In a power transmission device the combination of a driving shaft, a driven member, a variable speed hydraulic transmission for delivering power from the driving shaft to the driven member, a member movable to vary the mechanical advantage of the driving shaft upon the driven member, control means normally connected to operate said member and means responsive to the pressure in said transmission for moving said member and including means for disconnecting said normal control means.

16. In a power transmission device the combination of a driving shaft, a driven member, a variable speed hydraulic transmission for delivering power from the driving shaft to the driven member, a member movable to vary the mechanical advantage of the driving shaft upon the driven member, control means normally connected to operate said member and means responsive to the pressure in said transmission for moving said member, and including means for disconnecting said normal control means, and means movable with said member for varying the pressure response of said means. 

